At the recent request of high-density, high-integration semiconductor devices, it is required to form holes or trenches of a high aspect ratio (hereinafter, simply referred to as “deep trench (DT)”).
When forming deep trenches on a silicon (Si) layer by etching using plasma, for example, an oxide layer is used as a mask layer. In such an etching process of the silicon layer, increase in etching rate (“ER”) of the silicon layer causes increase in ER of the oxide layer. For this reason, selectivity of etching of the silicon layer can be enhanced and the remaining oxide layer becomes a rate limiting factor. Accordingly, it is impossible to obtain a sufficient etching depth. It was because etching of the silicon is impossible without the mask layer.
For example, Japanese Patent Application Publication No. 2003-056617 suggests a conventional etching technology employing a silicon layer as a target layer. In Japanese Patent Application Publication No. 2003-056617, there is disclosed a method of etching a silicon layer as a target object to form high-aspect ratio holes or trenches on the silicon layer, wherein HBr gas, O2 gas, and SiF gas are used as processing gases, and first high-frequency power of a first frequency and second high-frequency power of a second frequency are applied to a lower electrode for mounting the target object thereon in a substrate processing chamber.
However, the above-mentioned conventional technique fails to provide a satisfactory selectivity in etching the silicon layer with respect to the oxide layer.
In view of the above the present invention provides a substrate processing method for etching a silicon layer, which can enhance selectivity of etching the silicon layer with respect to an oxide layer serving as a mask layer.